Conventional surface protective layers and interlayer insulating layers for semiconductor devices can include a polyimide resin having excellent heat resistance, electrical characteristics, and mechanical characteristics, among other properties.
Surface protective layers, interlayer insulating layers, and the like including a polyimide resin have recently been formed using a photosensitive polyimide precursor composition. The polyimide precursor composition can be coated on a semiconductor device, patterned by ultraviolet (UV) radiation, developed, and heat imidized. Accordingly, it is possible to significantly shorten process times as compared to process times for conventional non-photosensitive polyimide precursor compositions.
The photosensitive polyimide precursor composition can be a positive type composition in which an exposed part is dissolved by development or a negative type composition in which the exposed part is cured and remains. Positive type photosensitive compositions can be advantageous because they can be developed using a non-toxic alkali aqueous solution.
The positive photosensitive polyimide precursor composition includes a polyimide precursor of polyamic acid and a photosensitive material of diazonaphtoquinone, among other components. However, the use of the positive photosensitive polyimide precursor composition can be problematic because the carbonic acid of the polyamidic acid can be so highly soluble in alkali that it is difficult to obtain a desired pattern.
In order to solve this problem, polyamidic acid can be esterified with an alcohol compound having at least one hydroxyl group to provide a material in which phenolic hydroxyl acid has been introduced instead of carbonic acid (refer to Japanese Patent Laid-Open Publication No H10-307393). This material, however, can be insufficiently developed, which can cause problems such as loss of layer thickness or resin delamination from the substrate.
Recently, a material in which a polybenzoxazole precursor is mixed with a diazonaphtoquinone compound has drawn attention (Japanese Patent Laid-open Publication No. S63-96162). When the polybenzoxazole precursor composition is actually used, however, layer thickness of an unexposed part can significantly decrease, which can make it difficult to obtain a desirable pattern after the developing process. Increasing the molecular weight of the polybenzoxazole precursor can reduce loss of layer thickness of the unexposed part, but development residue (scum) is generated which can deteriorate resolution and increase development times for the exposed part.
In order to solve these problems, it has been reported that loss of layer thickness can be suppressed by adding a certain phenol compound to a polybenzoxazole precursor composition (Japanese Patent Laid-Open Publication No. H9-302221 and Japanese Patent Laid-Open Publication No. 2000-292913). However, the effect of suppressing loss of layer thickness of the unexposed part is insufficient. Accordingly, there is still a need to improve the ability to suppress layer thinning (i.e., to reduce the loss of layer thickness), as well as to prevent the generation of development residue (scum).
In addition, phenols are added to regulate solubility, but they can be decomposed or cause a side reaction at high temperatures during thermal curing, which can significantly damage the mechanical properties of a cured film. Accordingly, there is still a need for a suitable dissolution controlling agent to replace conventional phenols.
Furthermore, when this polyimide or polybenzoxazole precursor composition is used to prepare a thermally cured film, the thermally cured film should have excellent mechanical properties such as tensile strength, elongation, and Young's modulus when it remains in a semiconductor device and acts as a surface protective layer. In particular, as methods for packaging a semiconductor continue to rapidly develop, polyimides and polybenzoxazoles used as surface protective layers should also have improved mechanical properties to complement such new developments. However, polyimide and polybenzoxazole precursors conventionally used in semiconductor devices tend to have insufficient mechanical properties, including insufficient elongation. Accordingly, in order to solve this problem, it has been reported that various additives can be added thereto or a precursor compound that is cross-linkable during the thermal curing can be used.
However, despite improvements in mechanical properties, such as elongation, there remains a need for methods that provide improved mechanical properties without deteriorating photo characteristics such as sensitivity, resolution, and the like.